Vacuum pump

ABSTRACT

A vacuum pump comprises: a rolling bearing configured to support a rotor shaft provided at a pump rotor; a lubrication fluid storage section configured to store lubrication fluid to be supplied to the rolling bearing; a MEMS element including, at a rotor-shaft-side lubrication fluid circulation path in a lubrication fluid circulation path between the rolling bearing and the lubrication fluid storage section, an infinitesimal flow rate pump configured to discharge a liquid droplet of the lubrication fluid; and a first flow path of a capillary structure configured to move the lubrication fluid of the lubrication fluid storage section to the infinitesimal flow rate pump by capillary force.

BACKGROUND OF THE INVENTION 1. Technical Field

The present invention relates to a vacuum pump.

2. Background Art

Typically, a vacuum pump configured such that a rotor is supported by a rolling bearing has been known (see, e.g., Patent Literature 1 (Japanese Patent No. 6162644). The vacuum pump described in Patent Literature 1 is a turbo-molecular pump, and a higher rotation speed is necessary for a smaller turbo-molecular pump having a smaller rotor blade diameter. In the rolling bearing used for high-speed rotation, an optimal lubricant supply amount is extremely small.

Typically, it is, as in the technique described in Patent Literature 1, configured such that a cone having a conical surface is attached to an axial end side of the rolling bearing and lubricant is supplied little by little from a flexible lubricant outflow section contacting the conical surface of the cone. The lubricant adhering to the conical surface is moved to a bearing side with an increased cone diameter by centrifugal force, and then, flows into the bearing. In the technique described in Patent Literature 1, an outlet of a lubricant flow path is closed with a flexible core to serve as the lubricant outflow section. The lubricant is supplied to the core by the pump, thereby causing the core to contact the conical surface of the cone. The lubricant transferred in the core is sent to the conical surface of the cone by capillary action.

However, there is a disadvantage that the state of contact of the core with the conical surface changes due to an error in assembly of the core with the conical surface of the cone and the amount of lubricant to be supplied changes due to the contact state. Moreover, there is a problem that supply of the lubricant is insufficient due to deterioration caused by, e.g., core friction due to contact with the conical surface.

SUMMARY OF THE INVENTION

A vacuum pump comprises: a rolling bearing configured to support a rotor shaft provided at a pump rotor; a lubrication fluid storage section configured to store lubrication fluid to be supplied to the rolling bearing; a MEMS element including, at a rotor-shaft-side lubrication fluid circulation path in a lubrication fluid circulation path between the rolling bearing and the lubrication fluid storage section, an infinitesimal flow rate pump configured to discharge a liquid droplet of the lubrication fluid; and a first flow path of a capillary structure configured to move the lubrication fluid of the lubrication fluid storage section to the infinitesimal flow rate pump by capillary force.

The vacuum pump further comprises: a lubrication path member provided adjacent to the rolling bearing at the rotor shaft and having a conical surface forming part of the lubrication fluid circulation path. A radius of the conical surface from a center of the rotor shaft is set greater toward the rolling bearing, and the lubrication fluid discharged from the infinitesimal flow rate pump and adhering to the conical surface is moved in a direction of the rolling bearing on the conical surface by centrifugal force.

The infinitesimal flow rate pump is configured to discharge the lubrication fluid to the rolling bearing.

The vacuum pump further comprises: at least one of a vibration sensor configured to detect vibration of the rolling bearing or a temperature sensor configured to perform non-contact detection of a temperature of the lubrication fluid circulation path; and a control section configured to drivably control the infinitesimal flow rate pump based on a detection result of at least one of the vibration sensor or the temperature sensor, thereby controlling an amount of the lubrication fluid to be transferred by the infinitesimal flow rate pump.

The vacuum pump further comprises: a warning section configured to output deterioration information on the rolling bearing based on the detection result of at least one of the vibration sensor or the temperature sensor.

The vacuum pump further comprises: a lubrication path member provided adjacent to the rolling bearing at the rotor shaft. The lubrication path member has a conical surface forming part of the lubrication fluid circulation path, and an axial end surface connected to the conical surface and forming another part of the lubrication fluid circulation path, and the MEMS element provided with the infinitesimal flow rate pump is arranged facing the axial end surface, and the liquid droplet of the lubrication fluid is discharged from the infinitesimal flow rate pump to the axial end surface.

The MEMS element has a temperature sensor configured to capture infrared light emitted from a surface of the rotor shaft or a surface of the lubrication path member as a temperature measurement target surface to measure a temperature, and an infrared light incident window that the infrared light guided by the temperature sensor enters, and a first protection section configured to prevent adherence of the lubrication fluid to the infrared light incident window is further provided.

The vacuum pump further comprises: a second protection section configured to prevent adherence to the temperature measurement target surface.

The vacuum pump further comprises: a flow rate sensor configured to detect an amount of the lubrication fluid to be transferred by the infinitesimal flow rate pump; and a diagnosis section configured to make a diagnosis on an amount of the lubrication fluid stored in the lubrication fluid storage section based on a detection result of the flow rate sensor.

According to the present invention, a proper amount of lubrication fluid can be stably supplied to a rolling bearing rotating at high speed in vacuum environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a pump main body of a turbo-molecular pump;

FIG. 2 is a view of a lubrication system of a bearing;

FIG. 3 is a view of a lubrication fluid delivery side of a MEMS element;

FIGS. 4A and 4B are views of an A-A section of FIG. 3;

FIGS. 5A and 5B are views of variations (a first variation, a second variation); and

FIG. 6 is a view of a second embodiment;

FIG. 7 is a view of a third embodiment;

FIG. 8 is a view of a third variation;

FIG. 9 is a view of a fourth variation;

FIG. 10 is a view of a fifth variation; and

FIG. 11 is a view in a case where a MEMS element provided only with an infinitesimal flow rate pump is arranged.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First Embodiment

FIG. 1 is a view of a first embodiment of a vacuum pump according to the present invention, and illustrates a section of a turbo-molecular pump 1. The turbo-molecular pump 1 includes a power device configured to supply power to a pump main body, but such a power device is not shown in FIG. 1.

The turbo-molecular pump 1 includes, as exhaust functions, a turbo pump section P1 having turbine blades, and a Holweck pump section P2 having a spiral groove. Needless to say, the present invention is not limited to the vacuum pump including the turbo pump section P1 and the Holweck pump section P2 as the exhaust functions, and is also applicable to a vacuum pump including only turbine blades, a vacuum pump including only a drag pump such as a Siegbahn pump or a Holweck pump, or a combination thereof.

The turbo pump section P1 includes multiple stages of rotor blades 30 formed at a pump rotor 3, and multiple stages of stationary blades 20 arranged on abase 2 side. On the other hand, the Holweck pump section P2 provided on an exhaust downstream side of the turbo pump section P1 includes a cylindrical portion 31 formed at the pump rotor 3, and a stator 21 arranged on the base 2 side. The spiral groove is formed at an inner peripheral surface of the cylindrical stator 21. The multiple stages of the rotor blades 30 and the cylindrical portion 31 forma rotary-side exhaust function, and the multiple stages of the stationary blades 20 and the stator 21 form a stationary-side exhaust function.

The pump rotor 3 is fastened to a shaft 10, and the shaft 10 is rotatably driven by a motor 4. For example, a DC brushless motor is used as the motor 4. A motor stator 4 a is provided at abase 2, and a motor rotor 4 b is provided on a shaft 10 side. A rotor unit RU including the shaft 10 and the pump rotor 3 is rotatably supported by a permanent magnet magnetic bearing 6 using permanent magnets 6 a, 6 b and a bearing 8 as a rolling bearing.

The permanent magnets 6 a, 6 b are ring-shaped permanent magnets magnetized in an axial direction. The multiple permanent magnets 6 a provided at the pump rotor 3 are arranged in the axial direction such that those with the same polarity face each other. On the other hand, the multiple stationary-side permanent magnets 6 b are attached to a magnet holder 11 fixed to a pump case 12. These multiple permanent magnets 6 b are also arranged in the axial direction such that those with the same polarity face each other.

The axial position of the permanent magnet 6 a provided at the pump rotor 3 is set slightly higher than the position of the permanent magnet 6 b arranged on an inner peripheral side of the permanent magnet 6 a. That is, the magnetic pole of the rotary-side permanent magnet is, by a predetermined amount, shifted in the axial direction with respect to the magnetic pole of the stationary-side permanent magnet. Depending on the magnitude of the predetermined amount, support force of the permanent magnet magnetic bearing 6 varies. In an example illustrated in FIG. 1, the permanent magnets 6 a are arranged on an upper side as viewed in the figure, and therefore, support force in a radial direction and upward (a direction toward a pump exhaust port) force in the axial direction act on the rotor unit RU due to repulsive force of the permanent magnets 6 a and the permanent magnets 6 b.

A bearing holder 13 configured to hold a bearing 9 is fixed to the center of the magnet holder 11. In FIG. 1, deep groove ball bearings are used as the bearings 8, 9, but the present invention is not limited to above. For example, angular contact bearings may be used. The bearing 9 functions as a touchdown bearing configured to limit radial runout of a shaft upper portion. In a steady rotation state, the shaft 10 and the bearing 9 do not contact each other. In a case where great disturbance is applied or whirling of the shaft 10 becomes greater upon acceleration or deceleration of rotation, the shaft 10 contacts the bearing 9.

The bearing 8 is held by a bearing holder 50 provided at the base 2. A lubrication fluid storage section 60 configured to store lubrication fluid to be supplied to the bearing 8 and a micro electro mechanical systems (MEMS) element 40 equipped with an infinitesimal flow rate pump configured to supply the lubrication fluid to the bearing 8 are provided at the bearing holder 50. Note that the MEMS is a device system configured such that a minute mechanical component, a sensor, an actuator, and the like and an electronic circuit are integrated on a single substrate (e.g., a silicon substrate, a glass substrate, or an organic material). Liquid lubricant such as lubricant oil is used as the lubrication fluid for the bearing 8.

FIG. 2 is a view of a lubrication system for the bearing 8, and illustrates a portion of the bearing holder 50 provided with the bearing 8 and the MEMS element 40 in detail. The bearing 8 includes an outer ring 81, an inner ring 82, a rolling body 83, and a holder 84. Rolling surfaces 811, 821 are formed at an inner peripheral surface of the outer ring 81 and an outer peripheral surface of the inner ring 82. A cone-shaped nut 100 is screwed into an external thread portion 10 a formed at a lower end of the shaft 10, and therefore, the inner ring 82 of the bearing 8 is fixed to the shaft 10. The outer ring 81 is held at the bearing holder 50. A radial damper 52 arranged on an outer peripheral side of the outer ring 81 is provided between the outer ring 81 and the bearing holder 50. For example, an elastic member of rubber is used as the radial damper 52.

The lubrication fluid storage section 60 is provided at a storage holder 51 fixed to a lower end (see FIG. 1) of the bearing holder 50. A lubrication fluid return section 62 made of a capillary material is provided between a lower end of the outer ring 81 and an upper end of the lubrication fluid storage section 60 in contact with both of the outer ring 81 and the lubrication fluid storage section 60. The lubrication fluid storage section 60 and the lubrication fluid return section 62 are made of a felt-like or sponge-like porous material, porous sintered plastic, or porous sintered metal, and the lubrication fluid is stored in many microvoids formed at the porous material. When the lubrication fluid contacts the porous material with many microvoids, the lubrication fluid penetrates the porous material and expands to a surrounding region due to capillary force. Such capillary force depends on microvoid spatial dimensions and wettability of an inner surface in a space as described later. A structure having sufficient capillary force for expanding the lubrication fluid across a flow path of the lubrication system will be referred to as a “capillary structure” in the present embodiment. Moreover, the felt-like or sponge-like porous material, the porous sintered plastic, the porous sintered metal and the like ensuring proper wettability will be referred to as the “capillary material.”

The MEMS element 40 is fixed to an inner peripheral surface of the storage holder 51 facing an outer peripheral surface 100 a of the cone-shaped nut 100. The outer peripheral surface 100 a of the cone-shaped nut 100 forms a conical surface, and is made of a material lyophilic to the lubrication fluid. The outer peripheral surface 100 a is set such that a radius from the center of the shaft 10 increases toward the bearing 8. The MEMS element 40 is equipped with an infinitesimal flow rate pump 401, and in the present embodiment, the lubrication fluid is supplied to the bearing 8 by the infinitesimal flow rate pump 401 incorporated into the MEMS element 40.

The MEMS element 40 is drivably controlled by a drive circuit 301 connected through a cable 42. In the present embodiment, the drive circuit 301 is provided at a power device 300 of the turbo-molecular pump, but may be provided on a pump main body side. The MEMS element 40 and the lubrication fluid storage section 60 are connected to each other through a suction tube 61 configured to guide the lubrication fluid of the lubrication fluid storage section 60 to the MEMS element 40 by the capillary force. The suction tube 61 is also made of the capillary material, and for example, a tube filled with the porous material such as felt is used.

The infinitesimal flow rate pump 401 is configured to discharge liquid droplets of the lubrication fluid supplied from the lubrication fluid storage section 60 to the outer peripheral surface 100 a of the cone-shaped nut 100. As described above, the outer peripheral surface 100 a is made of the lyophilic material, and therefore, the lubrication fluid adhering to the outer peripheral surface 100 a expands on the surface. As described above, the outer peripheral surface 100 a is set such that the radius from the center of the shaft 10 increases toward the bearing 8, and therefore, the lubrication fluid on the outer peripheral surface 100 a moves in the direction of increasing the radius by centrifugal force when the shaft 10 rotates at high speed. That is, the lubrication fluid on the outer peripheral surface 100 a moves in a bearing direction on the outer peripheral surface 100 a, and enters the inner ring 82. Part of the lubrication fluid having entered the inner ring 82 moves to the outer ring 81 through the rotating rolling body 83. The lubrication fluid expands across the rolling surfaces 811, 821 due to contact between each rolling surface 811, 821 and the rolling body 83, and is provided for lubrication of this portion. The lubrication fluid discharged from the rolling surface 811 of the outer ring 81 returns to the lubrication fluid storage section 60 through the lubrication fluid return section 62. As described above, the lubrication fluid circulates in a lubrication fluid circulation path R as indicated by a dashed arrow of FIG. 2.

FIG. 3 is a view of the MEMS element 40, the MEMS element 40 being viewed from a cone-shaped nut 100 side. As described above, the MEMS element 40 incorporates the infinitesimal flow rate pump 401, and is connected to the suction tube 61. A valve 403 is provided between a flow path 404 communicating with the suction tube 61 and a flow path 405 communicating with the infinitesimal flow rate pump 401. By opening/closing of the valve 403, connection/disconnection between the flow path 404 and the flow path 405 is controlled. The infinitesimal flow rate pump 401 discharges the liquid droplets of the lubrication fluid through a nozzle 402.

FIGS. 4A and 4B are views of an A-A section of FIG. 3. FIG. 4A illustrates a case where the valve 403 is in a closed state, and FIG. 4B illustrates a case where the valve 403 is in an open state. The infinitesimal flow rate pump 401 of the present embodiment illustrated in FIGS. 4A and 4B is a pump having such a structure that the lubrication fluid is transferred using a piezoelectric element. The type of infinitesimal flow rate pump using the piezoelectric element is a pump employing a method in which pressure is applied to an inflow fluid capacity (a pressure chamber) by a combination of a deflectable thin plate or a deflectable thin plate forming portion and the piezoelectric element to send out the fluid.

As illustrated in FIGS. 4A and 4B, the MEMS element 40 has such a structure that three layers of an upper layer 40A, an intermediate layer 40B, and a lower layer 40C are bonded to each other. Note that the upper layer 40A is indicated by a chain double-dashed line. The infinitesimal flow rate pump 401 includes a piezoelectric element 411, a diaphragm 412, and a pressure chamber 413. Voltage application to the piezoelectric element 411 is controlled by the drive circuit 301. An upper surface of the piezoelectric element 411 is fixed to the upper layer 40A, and a lower surface of the piezoelectric element 411 is fixed to the diaphragm 412. An opening 414 as an inlet of the nozzle 402 is formed at a location facing the diaphragm 412 at the pressure chamber 413. The opening 414 is formed in a conical shape expanding as extending toward a pressure chamber 413 side.

The valve 403 includes a valve body 415 having a diaphragm, a piezoelectric element 416 configured to drive the valve body 415, and a valve seat 417 provided at a location facing the valve body 415. Voltage application to the piezoelectric element 416 is controlled by the drive circuit 301. An upper surface of the piezoelectric element 416 is fixed to the upper layer 40A, and a lower surface of the piezoelectric element 416 is fixed to the valve body 415. In the state illustrated in FIG. 4A, the valve body 415 and the valve seat 417 are in close contact with each other, and the valve 403 is in the closed state. As a result, the flow path 404 and the flow path 405 are blocked from each other.

In the valve closed state illustrated in FIG. 4A, when voltage is applied to the piezoelectric element 411 of the infinitesimal flow rate pump 401, the lubrication fluid in the pressure chamber 413 is, as the liquid droplets, discharged from the nozzle 402. That is, when voltage is applied to the piezoelectric element 411, the piezoelectric element 411 is extended in an upper-to-lower direction as viewed in the figure, and the diaphragm 412 is pushed down as viewed in the figure to pressurize the pressure chamber 413. By such pressurization, part of the lubrication fluid in the pressure chamber 413 is discharged from the nozzle 402 through the opening 414. As described above, in the case of the configuration in which the liquid droplets of the lubrication fluid are discharged from the nozzle 402 formed at the MEMS element 40, a flow path surface to an outlet of the nozzle 402 is preferably made of a material exhibiting lyophilicity to the lubrication fluid and favorable wettability, and an outer portion (including an outer surface at the periphery of the outlet) with respect to the outlet is preferably made of a liquid-repellent material.

When the lubrication fluid is supplied to the pressure chamber 413 of the infinitesimal flow rate pump 401, voltage is applied to the piezoelectric element 416 of the valve 403 to bring the valve 403 into the open state as illustrated in FIG. 4B. When voltage is applied to the piezoelectric element 416, the piezoelectric element 416 is contracted in the upper-to-lower direction as illustrated in FIG. 4B to lift the valve body 415 upward. Accordingly, a clearance is formed between the valve body 415 and the valve seat 417, and therefore, the valve 403 is brought into the open state. As a result, the flow path 404 and the flow path 405 communicate with each other.

Note that a lubrication fluid circulation system including the bearing 8 and the lubrication fluid storage section 60 is in vacuum environment, and therefore, an atmospheric pressure difference cannot be utilized for movement of the lubrication fluid. For this reason, in the present embodiment, it is configured such that the capillary force in capillary action is utilized to move the lubrication fluid in the flow path 404 to the pressure chamber 413. That is, the dimensions of the flow paths 404, 405 and the pressure chamber 413 are set to such dimensions that proper capillary force is generated. Details of the capillary force will be described later.

Note that the type of infinitesimal flow rate pump 401 using the piezoelectric element has been described as an example with reference to FIGS. 4A and 4B, but the structure of the infinitesimal flow rate pump 401 is not limited to above. Other types of infinitesimal flow rate pumps may be applied. For example, one employing a method in which part of a sealed fluid capacity is rapidly heated to vaporization to generate bubbles and a volume is accordingly increased to push out the fluid (a liquified portion) and one employing a method in which potential is provided to a surface facing a charged thin plate (diaphragm) to displace the thin plate by repulsive force or attraction force due to static electricity and fluid is accordingly sucked or pushed out have been known as the infinitesimal flow rate pump incorporated into the MEMS element 40.

For the bearing 8 supporting the shaft 10 rotating at high speed, a lubrication state is the best, in which an agitation loss of the lubrication fluid is reduced as much as possible for reducing heat generation and contact between solids due to a broken lubrication fluid film is avoided upon rolling of the rolling body 83. Thus, an ideal thickness of the lubrication fluid film present on the rolling surfaces 811, 821 of the bearing 8 and the surface of the rolling body 83 of the bearing 8 is about several times as great as the surface roughness of these surfaces. For example, in a case where the rolling surfaces 811, 821 and the surface of the rolling body 83 are finished with a root-mean-square roughness R_(q) of 0.04 μm, the thickness of the lubrication fluid film is preferably about 0.12 to 0.20 μm.

As described above, the lubrication fluid having entered the bearing 8 is decreased little by little due to, e.g., outflow from an end portion of the outer ring 81, and for compensating for such a decrement, the lubrication fluid is supplied by the infinitesimal flow rate pump 401. In a case where an oil film having a thickness of equal to or less than 1 μm is formed at each spot in the bearing 8, the amount of lubrication fluid present in the bearing 8 is about several mg (equivalent to several μL (microliters) in terms of a volume). An outflow amount per second varies according to the structure of a portion from which the lubrication fluid flows out, but for example, is about 1/100 to 1/10000 of the amount of lubrication fluid accumulated in the bearing 8. Thus, this amount of lubrication fluid (a slight amount of several nL (nanoliters) per second or less) is supplied so that the thickness of the lubrication fluid film can be favorably maintained. In the present embodiment, for supplying a slight amount of lubrication fluid such as several nL (nanoliters) per second or less to the bearing 8, the infinitesimal flow rate pump 401 incorporated into the MEMS element 40 is used.

(Lubrication Fluid Circulation System)

In the lubrication fluid circulation system illustrated in FIG. 2, the lubrication fluid of the lubrication fluid storage section 60 circulates in the order of the lubrication fluid storage section 60, the suction tube 61, the MEMS element 40, the outer peripheral surface 100 a, the bearing 8, the lubrication fluid return section 62, and the lubrication fluid storage section 60. Of this lubrication fluid circulation path R, at least a flow path from the lubrication fluid storage section 60 to the infinitesimal flow rate pump 401 of the MEMS element 40 utilizes the capillary force for movement of the lubrication fluid. In the lubrication fluid return section 62, the force of gravity can be utilized to return the lubrication fluid to the lubrication fluid storage section 60. However, the lubrication fluid return section 62 is made of the capillary material to utilize the capillary force, and therefore, the lubrication fluid can be returned to the lubrication fluid storage section 60 regardless of a pump posture.

Pressure calculated according to Expression (1) below acts on a vacuum interface of the lubrication fluid in a capillary tube with an inner diameter d. Note that T indicates a tension (N/m) on the vacuum interface of the lubrication fluid, and θ indicates a contact angle representing wettability of a contact surface for the lubrication fluid. In this case, when the capillary tube stands along the direction of the force of gravity, the interface moves upward to a height h of (4T cos θ)/μgd. Note that ρ indicates a liquid density and g indicates a gravitational acceleration. That is, in the capillary material such as a thin tube or felt, the lubrication fluid moves (penetrates) and expands across the capillary material due to the capillary force.

(4T cos θ)/d  (1)

For example, in a case where a member having a contact angle θ of 15° is used as a material with favorable wettability and a flow path has an inner diameter d of 1.0×10⁻⁵ m=10 and a case where lubrication fluid having a surface tension T of 2.6×10⁻² N/m is used, the capillary force of Expression (1) is a pressure of about 10 kPa. When the density of the lubrication fluid is ρ=1000 kg/m³ and the gravitational acceleration is g=9.8 m/s², the height h of the interface of the lubrication fluid in the capillary tube under the force of gravity is about 100 cm.

In the case of using the capillary material for the lubrication fluid storage section 60 and the lubrication fluid return section 62 in the lubrication fluid circulation system illustrated in FIG. 2, a void diameter dimension (in the case of the porous material) and a fiber clearance (in the case of felt and the like) correspond to the above-described inner diameter d of the capillary tube. In the present embodiment, these dimensions are set to equal to or less than such values that proper capillary force is generated. Moreover, the dimensions of the flow paths 404 to 406 and the pressure chamber 413 formed at the MEMS element 40 are also set to equal to or less than values corresponding to the inner diameter d. The MEMS element 40 has a fine structure, and therefore, these conditions are fully satisfied in this case. Further, for the suction tube 61, the inner diameter of the suction tube 61 may be set to the above-described inner diameter d, or a capillary material, such as felt, filling a thick tube may be used. As described above, the clearance dimensions in the path for circulating the lubrication fluid are set to such dimensions that sufficient capillary force is generated, and therefore, the lubrication fluid can be properly supplied by the infinitesimal flow rate pump 401.

The amount of lubrication fluid to be supplied to the bearing 8 by the infinitesimal flow rate pump 401 is about several nL (nanoliters) per second as described above. In an infinitesimal flow rate pump used for, e.g., an inkjet head of a printer as described in Japanese Patent No. 3171958, a picoliter-order slight amount can be discharged per pulse. For example, in a case where the infinitesimal flow rate pump 401 is a pump configured so that 10 picoliters can be transferred per pulse, if the lubrication fluid is transferred with 100 pulses per second, a supply amount is 2 nanoliters. That is, the infinitesimal flow rate pump 401 incorporated into the MEMS element 40 is used so that a nanoliter-order slight amount of lubrication fluid per second can be supplied to the bearing 8. Note that the supply amount (the transfer amount) of the lubrication fluid by the infinitesimal flow rate pump 401 can be adjusted in such a manner that the frequency of stretching vibration of the piezoelectric element 411 is controlled by the drive circuit 301.

Note that as clearly seen from Expression (1), not only the dimensions of the capillary tube and the surface tension of the fluid interface but also the wettability of the surface contacting the fluid are important factor for determining the capillary force. Generally, as clearly seen from the fact that degreasing processing needs to be performed for a wafer material, such as monocrystal silicon, used for the MEMS element 40 before chemical processing for a surface, the wafer material basically exhibits lipophilicity (favorable wettability). However, in a case where an oleophobic substance as a coating adheres to the surface in the middle of a processing step, the wettability is extremely degraded. For this reason, at the processing step for the MEMS element 40, the step of avoiding an oleophobic (liquid-repellent) substance from adhering to an inner surface of the flow path is employed so that favorable wettability can be realized.

As described above, in the present embodiment, the MEMS element 40 provided with the infinitesimal flow rate pump 401 is provided, and the lubrication fluid is, by the capillary force, moved from the lubrication fluid storage section 60 to the infinitesimal flow rate pump 401 through the suction tube 61 as the capillary material. Moreover, the infinitesimal flow rate pump 401 discharges the liquid droplets of the lubrication fluid to the rolling body 83 and the holder 84 as the rotary-side lubrication fluid circulation path R. As a result, a slight amount of lubrication fluid can be stably supplied to the bearing in the vacuum environment.

(Variations)

In the above-described embodiment, it is configured such that the liquid droplets of the lubrication fluid are discharged to the outer peripheral surface 100 a of the cone-shaped nut 100 as one of the rotor-shaft-side lubrication fluid circulation paths, but the lubrication fluid may be discharged to a lubrication fluid circulation path in other regions. In a first variation illustrated in FIG. 5A, the lubrication fluid is discharged from the infinitesimal flow rate pump 401 of the MEMS element 40 provided at the storage holder 51 to the rolling body 83 and the holder 84 of the bearing 8 as part of the rotary-side lubrication fluid circulation path. The lubrication fluid adhering to the rolling body 83 and the holder 84 also adheres to the rolling surfaces 811, 821 of the outer ring 81 and the inner ring 82 in association with rotation of the bearing 8, and is provided for lubrication of this portion. That is, the lubrication fluid circulates along the lubrication fluid circulation path R indicated by the dashed arrow.

FIG. 5B is a view of a second variation, and the lubrication fluid is discharged from the infinitesimal flow rate pump 401 of the MEMS element 40 provided at the bearing holder 50 to the rolling body 83 and the holder 84 of the bearing 8 as part of the rotor-shaft-side lubrication fluid circulation path. In this case, the lubrication fluid adhering to the rolling body 83 and the holder 84 also adheres to the rolling surfaces 811, 821 of the outer ring 81 and the inner ring 82 in association with rotation of the bearing 8, and is provided for lubrication of this portion. In the configurations illustrated in FIGS. 5A and 5B, the cone-shaped nut 100 provided with the conical outer peripheral surface 100 a as illustrated in FIG. 2 is not necessarily used, and the inner ring 82 is merely fixed with a nut 110.

Second Embodiment

FIG. 6 is a view of a second embodiment. In the above-described first embodiment, the MEMS element 40 includes, as illustrated in FIG. 3, the infinitesimal flow rate pump 401 and the valve 403 as the lubrication fluid circulation system, for example. On the other hand, in the second embodiment, a MEMS element 40 includes, in addition to a lubrication fluid circulation system 430 having an infinitesimal flow rate pump 401 and a valve 403, a flow rate sensor 431, a temperature sensor 432, and a vibration sensor 433 such as an acceleration sensor. Note that in an example illustrated in FIG. 6, all of the flow rate sensor 431, the temperature sensor 432, and the vibration sensor 433 are provided, but it may be configured such that at least one of these sensors is provided as necessary.

The flow rate sensor 431 is configured to measure the flow rate of lubrication fluid flowing in a flow path 404, i.e., the flow rate of lubrication fluid flowing from a suction tube 61 to the infinitesimal flow rate pump 401. The temperature sensor 432 is configured to measure a temperature regarding a bearing 8. The vibration sensor 433 is configured to measure vibration generated at the bearing 8. The temperature sensor 432 may include one utilizing a thermocouple or a thermopile, and those employing other measurement methods.

Note that the thermocouple is a temperature sensor employing the method for measuring the temperature of a target object contacting the temperature sensor. Thus, in a case where the thermocouple is used as the temperature sensor 432 mounted in the MEMS element 40 arranged as in FIG. 2 and FIGS. 5A and 5B, the temperature of a storage holder 51 or a bearing holder 50 attached to the MEMS element 40 is directly measured, and the temperature of the bearing 8 is estimated from the measured temperature. Thus, in the case of such a configuration, the thermopile as a non-contact temperature sensor configured to detect radiation form a measurement target object to measure a temperature is preferably used as the temperature sensor 432.

In a case where an infrared light window for guiding infrared light from the measurement target to the thermopile as the temperature sensor 432 is formed at a surface of the MEMS element 40 on a side provided with a nozzle opening (a lubrication fluid discharge port) of the infinitesimal flow rate pump 401 or other surfaces of the MEMS element 40, the temperature measurement target is a member facing the MEMS element 40. For example, in the case of FIG. 2, the infrared light window for the temperature sensor 432 is provided at a portion of the MEMS element 40 indicated by a reference character S1 such that the temperature of a cone-shaped nut 100 is measured. In the case of the configuration of FIG. 5A, the infrared light window for the temperature sensor 432 is provided at a portion of the MEMS element 40 indicated by a reference character S2 such that the temperature of a cylindrical surface 110 a of an opposing nut 110 is measured. In the case of the configuration of FIG. 5B, the infrared light window for the temperature sensor 432 is provided at a portion of the MEMS element 40 indicated by a reference character S3 such that the temperature of an opposing surface 10 b of an opposing shaft 10 is measured.

As described above, the configuration in which the MEMS element is equipped with the flow rate sensor, the temperature sensor, the vibration sensor and the like is well-known. For example, one employing a method in which a change in a capacitance due to a change in a specific clearance state in association with an acceleration or vibration is detected as disclosed in JP-A-5-25687 and Japanese Patent No. 4804468 can be utilized as the vibration sensor 433. For example, one employing a method in which movement of heat generated due to movement of fluid is measured as disclosed in JP-A-6-066613 can be utilized as the flow rate sensor 431.

A power device 300 includes a drive circuit 301 configured to drivably control the infinitesimal flow rate pump 401 and the valve 403, and an arithmetic circuit 302 to which measurement signals from the flow rate sensor 431, the temperature sensor 432, and the vibration sensor 433 are input. The arithmetic circuit 302 is configured to make a diagnosis regarding the lubrication fluid for the bearing 8 based on the input measurement signals.

In the arithmetic circuit 302, the state of lubrication in the bearing 8 is estimated from a change in the temperature of an outer ring 81 and characteristics of vibration generated at the outer ring 81. As illustrated in FIG. 2, the bearing 8 is a ball bearing using a spherical body as a rolling body 83. Contact between a ball of the ball bearing and a rolling surface of each of inner and outer rings is partially “slipping” contact. In general terms, metal contact in which an oil film is present between contact surfaces shows multiple forms represented by a so-called Stribeck curve in the order of a boundary lubrication region, a mixed lubrication region, and a fluid lubrication region according to a ratio between the thickness of the present oil film and a surface roughness representative value of a metal surface.

It is demanded for the bearing 8 of the turbo-molecular pump illustrated in FIG. 1 that operation is performed with a state closest possible to the mixed lubrication region in the fluid lubrication region being maintained. In this region, a friction coefficient is the minimum, and a rotation loss of the bearing can be suppressed low. On the other hand, in the mixed lubrication region, there is a probability that metal contact is caused due to a broken lubricant oil film and, e.g., a sudden increase in the loss or galling is caused. Moreover, as the lubricant oil film is thickened, agitation resistance of lubricant oil is increased, and therefore, the rotation loss is increased.

For these reasons, in the arithmetic circuit 302, an increase or decrease in the thickness of the lubricant oil film on the rolling surface is estimated from the characteristics of vibration caused due to rolling of the rolling body. For example, in a case where the lubricant oil film thickness is a proper state (a normal state), when vibration data of the vibration sensor 433 is processed by FFT, peaks are shown at a vibration frequency corresponding to a rotor rotation frequency and multiples thereof and a vibration frequency corresponding to a component (the outer ring 81, an inner ring 82, the rolling body 83, and a holder 84) of the bearing 8. However, when the lubricant oil film thickness decreases to reach the mixed lubrication region, sudden vibration such as impact noise caused due to contact between protruding portions of metal surfaces is observed at a point different from the above-described vibration frequencies of the peaks, and the peak value of the vibration frequency corresponding to the component of the bearing 8 increases. Thus, it can be estimated that the amount of lubrication fluid becomes less than a proper amount due to occurrence of the sudden vibration.

In a case where the temperature sensor 432 is also equipped as in FIG. 6, a sharp temperature increase due to contact between the protruding portions of the metal surfaces upon a lubrication fluid decrease is also often observed. Thus, in a case where occurrence of the sudden vibration and the temperature increase have been observed or either one of occurrence of the sudden vibration or the sharp temperature increase has been observed, it can be estimated that the lubrication fluid amount has decreased.

On the other hand, an agitation phenomenon becomes noticeable when the lubricant oil film is thickened, and a phenomenon in which an amplitude in a specific frequency range (a range of several kHz) of vibration occurred at the outer ring 81 increases as a whole is observed. For example, an amplitude in a frequency range three to seven times as high as the vibration frequency corresponding to the rotor rotation frequency increases as a whole. For example, when a thick portion of the lubricant oil film is present on part of the outer ring rolling surface, this frequency is substantially close to a value obtained by multiplication of a ball revolution frequency by the number of balls. In the case of an agitation loss, characteristics that the entirety of a portion in the vicinity of a frequency corresponding to such a loss rises are observed. It is assumed that this is because a location where agitation occurs is shifted or a resistance value received by each ball changes accordingly. In this case, if the temperature sensor 432 is equipped, a temperature increase is observed when the lubrication fluid increases and an agitation decrease becomes noticeable. Thus, in a case where occurrence of the vibration with a specific frequency and the temperature increase have been observed, it can be estimated that the lubrication fluid amount is excessive.

The arithmetic circuit 302 performs the above-described analysis based on measurement data of the vibration sensor 433 or measurement data of the vibration sensor 433 and the temperature sensor 432, thereby making a diagnosis on a lubrication fluid amount decrease and excess of the lubrication fluid amount. This diagnosis result is output to the drive circuit 301 and a monitoring device 1000. The drive circuit 301 having received the diagnosis result increases the amount of lubrication fluid to be supplied by the infinitesimal flow rate pump 401 in a case where the lubrication fluid amount has decreased as compared to the proper amount. Conversely, in the case of an excessive lubrication fluid amount, supply of the lubrication fluid by the infinitesimal flow rate pump 401 is decreased or stopped such that the lubrication fluid amount for the bearing 8 is adjusted to the proper amount.

The measurement data of the vibration sensor 433 can be utilized not only for the diagnosis on the flow rate of the lubrication fluid but also for diagnosis on deterioration of the bearing 8. In a case where the bearing 8 has been deteriorated, a situation in which the amplitude is increased across the entire frequency and an increase in the amplitude of the frequency corresponding to the component of the deteriorated bearing 8 are generally observed. In a case where a scratch is caused on the rolling surface or a foreign object has entered the rolling surface, the vibration peak is often shown at a specific frequency as the function of the rotation frequency. Similarly, when the temperature of a portion at a location close to the bearing inner ring is monitored by the temperature sensor 432, a radiation destination of such a portion is limited, and therefore, a gradually-increasing temperature change due to a gradual increase in rotation resistance in association with deterioration of the inside of the bearing can be grasped. Thus, in a case where such a vibration situation has been observed from the vibration data or a gradual temperature increase phenomenon has been observed in the vicinity of the bearing inner ring, the arithmetic circuit 302 outputs, to the monitoring device 1000, a warning signal for informing deterioration of the bearing 8, thereby prompting the monitoring device 1000 to perform repair and maintenance. By such operation, deterioration of the bearing 8 can be properly handled, and therefore, e.g., occurrence of pump failure due to bearing deterioration can be prevented.

In a case where the lubrication fluid storage section 60 lacks the amount of stored lubrication fluid, even if the infinitesimal flow rate pump 401 is normally operated, the flow rate detected by the flow rate sensor 431 is less than a proper amount. When operation of the vacuum pump is continued in this state, occurrence of serious breakdown is predicted. Thus, the arithmetic circuit 302 makes a diagnosis on the amount of lubrication fluid stored in the lubrication fluid storage section 60 based on a detection result of the flow rate sensor 431, and outputs such a diagnosis result (i.e., the signal indicating the necessity of repair and maintenance) to the monitoring device 1000 to prompt the monitoring device 1000 to respond properly. By such operation, failure due to a lack of lubrication fluid in the lubrication fluid storage section 60 can be avoided.

As described above, in the second embodiment, the infinitesimal flow rate pump 401 is drivably controlled based on a detection result of at least either one of the vibration sensor 433 configured to detect vibration of the bearing 8 or the temperature sensor 432, and in this manner, the amount of transferred lubrication fluid is controlled. Thus, the lubrication fluid amount in the bearing 8 can be maintained at the proper amount without causing an excessive or deficient state. Note that deterioration of the bearing 8 is diagnosed so that occurrence of failure due to bearing deterioration can be prevented.

Third Embodiment

FIG. 7 is a view of a third embodiment. In the above-described example illustrated in FIG. 1, it is configured such that the liquid droplets of the lubrication fluid are discharged to the outer peripheral surface 100 a forming the conical surface of the cone-shaped nut 100. In the example illustrated in FIGS. 5A and 5B, it is configured such that the lubrication fluid is discharged to the bearing 8.

An infinitesimal flow rate pump 401 formed at a MEMS element 40 can accurately discharge a slight amount of lubrication fluid, and therefore, when the entirety of the lubrication fluid discharged from the infinitesimal flow rate pump 401 reaches the bearing 8, the amount of lubrication fluid supplied to the bearing 8 can be accurately controlled. Thus, all liquid droplets of the lubrication fluid discharged from the infinitesimal flow rate pump 401 need to reliably adhere to the outer peripheral surface 100 a of the cone-shaped nut 100.

Since a shaft 10 of a turbo-molecular pump 1 rotates at high speed, a relative speed between the outer peripheral surface 100 a of the cone-shaped nut 100 and the liquid droplet discharged from the infinitesimal flow rate pump 401 of the MEMS element 40 fixed to a base side is high. Thus, some of the liquid droplets of the lubrication fluid are blown away by the outer peripheral surface 100 a, and therefore, there is a probability that part of the lubrication fluid discharged from the infinitesimal flow rate pump 401 is not supplied to the bearing 8. Even when the amount of lubrication fluid discharged from the infinitesimal flow rate pump 401 is controlled with high accuracy, if there is an uncertain decrease (deviation from a lubrication fluid circulation path) in the lubrication fluid until the lubrication fluid reaches the bearing 8 after having been discharged from the infinitesimal flow rate pump 401, it is difficult to ensure a proper lubrication fluid supply state for maintaining a bearing rotation state with a low loss.

For these reasons, in the third embodiment, it is configured such that the infinitesimal flow rate pump 401 of the MEMS element 40 is arranged facing an axial end surface 100 b of the cone-shaped nut 100 and the liquid droplets of the lubrication fluid are discharged to the axial end surface 100 b. At the cone-shaped nut 100 rotating at high speed, the peripheral speed of the axial end surface 100 b is lower than the peripheral speed of the outer peripheral surface 100 a, and therefore, a relative speed between the liquid droplet and the axial end surface 100 b can be decreased as compared to the configuration illustrated in FIG. 2. Thus, the amount of liquid droplets blown away without adhering to the axial end surface 100 b can be reduced. The lubrication fluid adhering to the axial end surface 100 b moves in an outer edge direction of the axial end surface 100 b by centrifugal force, and thereafter, moves to the outer peripheral surface 100 a. Then, the lubrication fluid moves in the direction of the bearing 8 on the outer peripheral surface 100 a. Note that for reducing the relative speed between the liquid droplet and the axial end surface 100 b as much as possible, the liquid droplets are preferably discharged to a region of the axial end surface 100 b close to a rotor shaft.

A hexagonal hole 100 c is formed to penetrate the center of the cone-shaped nut 100. When the cone-shaped nut 100 is fixed to an external thread portion 10 a of the shaft 10, a tool such as a hexagonal wrench is inserted into the hexagonal hole 100 c to fasten the cone-shaped nut 100. The MEMS element 40 is, as described above, configured such that the infinitesimal flow rate pump 401 faces the axial end surface 100 b and an infrared light window 432 a of a temperature sensor 432 faces the hexagonal hole 100 c. That is, the temperature sensor 432 is configured to detect infrared light discharged from an end surface 101 of the external thread portion 10 a of the shaft 10 to monitor the temperature of the shaft 10.

At the MEMS element 40, a tubular protection section 440 is provided to surround the periphery of the infrared light window 432 a. The protection section 440 is a member configured to prevent the liquid droplets of the lubrication fluid discharged from the infinitesimal flow rate pump 401 from adhering to the infrared light window 432 a. When the liquid droplets adhere to the infrared light window 432 a, it is difficult to accurately measure a temperature by the temperature sensor 432. For this reason, the protection section 440 is provided such that the infrared light window 432 a is not viewed from the infinitesimal flow rate pump 401 configured to discharge the liquid droplets and the axial end surface 100 b with the probability of blowing away the liquid droplets. The protection section 440 can prevent the incoming liquid droplets discharged from the infinitesimal flow rate pump 401 from adhering to the infrared light window 432 a. If the liquid droplets are blown away by the axial end surface 100 b, these liquid droplets are blocked by the protection section 440, and therefore, there is no probability that the blown-away liquid droplets adhere to the infrared light window 432 a.

Note that only for preventing the incoming liquid droplets from the infinitesimal flow rate pump 401 and the axial end surface 100 b, it is enough that the axial position of a tip end of the protection section 440 is at the substantially same position as that of the axial end surface 100 b. In an example illustrated in FIG. 7, the height dimension of the protection section 440 is set to such a dimension that the tip end of the protection section 440 is inserted into the inside of the hexagonal hole 100 c. The protection section 440 is inserted into the inside of the hexagonal hole 100 c as described above, and therefore, the end surface 101 of the shaft 10 cannot be viewed from the infinitesimal flow rate pump 401. This can prevent the liquid droplets of the lubrication fluid discharged from the infinitesimal flow rate pump 401 from adhering to the end surface 101 of the shaft 10 as a temperature measurement target surface.

When the lubrication fluid adheres to the temperature measurement target surface, the state of infrared light emitted from the temperature measurement target surface changes, and the accuracy of a temperature measurement value is degraded. In the example illustrated in FIG. 7, the protection section 440 is inserted into the hexagonal hole 100 c so that adherence of the lubrication fluid to the temperature measurement target surface can be prevented and degradation of the accuracy of the temperature measurement value can be prevented. Note that the amount of insertion of the protection section 440 into the hexagonal hole 100 c is set as necessary considering, e.g., clearance dimensions between the protection section 440 and the hexagonal hole 100 c.

In the example illustrated in FIG. 7, a hole penetrating an end portion provided with the axial end surface 100 b of the cone-shaped nut 100 is the hexagonal hole 100 c, and the hexagonal hole 100 c is also utilized for fastening of the cone-shaped nut 100. However, in the case of a configuration in which other portions than the through-hole are utilized for fastening, the through-hole is not limited to the hexagonal hole. In FIG. 7, the axial end surface 100 b of the cone-shaped nut 100 is illustrated as a plane perpendicular to the rotor shaft, but is not limited to the plane. For example, the axial end surface 100 b may be a gently-tapered surface (a surface forming a flat side surface of a cone), or may be a curved surface forming part of a curved surface connected to the outer peripheral surface 100 a and having a gentle curvature.

(Third Variation)

FIG. 8 is a view of a third variation as a variation of the third embodiment illustrated in FIG. 7. In the third variation, a step Δh is provided between a surface (hereinafter referred to as a “discharge surface”) 410 of the MEMS element 40 to which the liquid droplets of the lubrication fluid is discharged and a surface 419 of the MEMS element 40 provided with the infrared light window 432 a, and the protection section 440 is fixed to the cone-shaped nut 100. The step Δh is set greater than the protruding amount of the infrared light window 432 a, and is configured such that the infrared light window 432 a is not viewed from the discharge surface 410. Further, due to the presence of the protection section 440, the infrared light window 432 a cannot be viewed from the axial end surface 100 b. Moreover, since the protection section 440 is provided, the end surface 101 of the cone-shaped nut 100 cannot be viewed from the discharge surface 410.

The configuration illustrated in FIG. 8 can prevent the lubrication fluid from adhering to the infrared light window 432 a and the end surface 101 of the shaft 10. Specifically, in the third variation, no clearance is formed between the protection section 440 and the through-hole (the hexagonal hole) of the cone-shaped nut 100 as in the configuration of FIG. 7, and therefore, this can reliably prevent the liquid droplets of the lubrication fluid discharged from the infinitesimal flow rate pump 401 form adhering to the end surface 101.

(Fourth Variation)

Note that in the examples illustrated in FIGS. 7 and 8, the hexagonal hole 100 c penetrating the cone-shaped nut 100 is formed. However, a recessed portion 100 d may be formed at the end surface of the cone-shaped nut 100 as in a fourth variation illustrated in FIG. 9, and the protection section 440 may be fixed to the recessed portion 100 d. The configuration of the MEMS element 40 is similar to that of the MEMS element 40 illustrated in FIG. 8. In this case, the temperature sensor 432 detects infrared light emitted from a bottom surface of the recessed portion 100 d to measure the temperature of the cone-shaped nut 100.

(Fifth Variation)

FIG. 10 is a view of a fifth variation. In the fifth variation, a hexagonal columnar raised portion 100 e is formed at the axial end surface 100 b of the cone-shaped nut 100. The configuration of the MEMS element 40 is similar to those of the MEMS elements 40 illustrated in FIGS. 8 and 9. The raised portion 100 e is formed such that a tip end surface of the raised portion 100 e is on the substantially same plane as that of the discharge surface 410 or is on an infrared light window 432 a side with respect to the discharge surface 410. The temperature sensor 432 faces the raised portion 100 e, and detects infrared light emitted from a surface (the tip end surface) of the raised portion 100 e to measure the temperature of the cone-shaped nut 100.

In the configuration illustrated in FIG. 10, the step Δh is formed at the MEMS element 40, and therefore, the infrared light window 432 a cannot be viewed from the discharge surface 410. Moreover, an end surface 102 of the raised portion 100 e as the measurement target surface of the temperature sensor 432 cannot be viewed from the discharge surface 410. This can prevent the liquid droplets of the lubrication fluid discharged from the infinitesimal flow rate pump 401 from adhering to the infrared light window 432 a and the end surface 102 of the raised portion 100 e. Further, due to the presence of the raised portion 100 e, the infrared light window 432 a cannot be viewed from the axial end surface 100 b. Thus, if the liquid droplets are blown away by the axial end surface 100 b, no liquid drops adhere to the infrared light window 432 a.

Note that the hexagonal columnar raised portion 100 e is utilized for fastening the cone-shaped nut 100. However, in the case of a configuration in which other portions than the through-hole are utilized for fastening, the raised portion 100 e is not limited to the hexagonal column, and for example, may a circular column. Alternatively, as illustrated in FIG. 11, only the infinitesimal flow rate pump 401 is provided at the MEMS element 40 arranged facing the axial end surface 100 b of the cone-shaped nut 100. Although the temperature sensor is not shown in the figure, the temperature sensor is arranged at another position different from that of the MEMS element 40.

The multiple example embodiments and variations described above are understood as specific examples of the following aspects by those skilled in the art.

[1] a vacuum pump according to one aspect includes a rolling bearing configured to support a rotor shaft provided at a pump rotor, a lubrication fluid storage section configured to store lubrication fluid to be supplied to the rolling bearing, a MEMS element including, at a rotor-shaft-side lubrication fluid circulation path in a lubrication fluid circulation path between the rolling bearing and the lubrication fluid storage section, an infinitesimal flow rate pump configured to discharge a liquid droplet of the lubrication fluid, and a first flow path of a capillary structure configured to move the lubrication fluid of the lubrication fluid storage section to the infinitesimal flow rate pump by capillary force.

As illustrated in FIG. 2, the lubrication fluid of the lubrication fluid storage section 60 is moved to the infinitesimal flow rate pump 401 formed at the MEMS element 40 by the suction tube 61 as the flow path of the capillary structure, and in the form of the liquid droplet, is discharged from the infinitesimal flow rate pump 401 to the outer peripheral surface 100 a of the cone-shaped nut 100 as part of the lubrication fluid circulation path. As a result, a proper amount of lubrication fluid can be stably supplied to the bearing 8.

[2] The vacuum pump according to [1] further includes a lubrication path member provided adjacent to the rolling bearing at the rotor shaft and having a conical surface forming part of the lubrication fluid circulation path. The radius of the conical surface from the center of the rotor shaft is set greater toward the rolling bearing, and the lubrication fluid discharged from the infinitesimal flow rate pump and adhering to the conical surface is moved in the direction of the rolling bearing on the conical surface by centrifugal force.

As illustrated in FIG. 2, the outer peripheral surface 100 a of the cone-shaped nut 100 is formed by the conical surface, and the radius of the conical surface from the center of the shaft 10 is set greater toward the bearing 8 so that the lubrication fluid adhering to the outer peripheral surface 100 a can be effectively moved in the direction of the bearing 8 by the centrifugal force.

[3] In the vacuum pump according to [1], the infinitesimal flow rate pump is configured to discharge the lubrication fluid to the rolling bearing. As illustrated in FIG. 5A or FIG. 5B, the lubrication fluid may be discharged from the infinitesimal flow rate pump 401 to the bearing 8, and in this case, the cone-shaped nut 100 having the conical outer peripheral surface 100 a is not necessary.

[4] The vacuum pump according to any one of [1] to [3] further includes at least one of a vibration sensor configured to detect vibration of the rolling bearing or a temperature sensor configured to perform non-contact detection of the temperature of the lubrication fluid circulation path, and a control section configured to drivably control the infinitesimal flow rate pump based on a detection result of at least one of the vibration sensor or the temperature sensor, thereby controlling the amount of the lubrication fluid to be transferred by the infinitesimal flow rate pump. As illustrated in FIG. 6, the infinitesimal flow rate pump 401 is drivably controlled based on the detection result of at least one of the vibration sensor 433 and the temperature sensor 432 to control the amount of lubrication fluid to be transferred, and therefore, a proper amount of lubrication fluid can be supplied according to the status of the bearing 8.

[5] The vacuum pump according to [4] further includes a warning section configured to output deterioration information on the rolling bearing based on the detection result of at least one of the vibration sensor or the temperature sensor. An appropriate response can be made to the rolling bearing based on the deterioration information output from the warning section.

[6] The vacuum pump according to [1] further includes a lubrication path member provided adjacent to the rolling bearing at the rotor shaft. The lubrication path member has a conical surface forming part of the lubrication fluid circulation path, and an axial end surface connected to the conical surface and forming another part of the lubrication fluid circulation path. The MEMS element provided with the infinitesimal flow rate pump is arranged facing the axial end surface, and the liquid droplet of the lubrication fluid is discharged from the infinitesimal flow rate pump to the axial end surface.

As illustrated in FIG. 7, the MEMS element 40 provided with the infinitesimal flow rate pump 401 is arranged facing the axial end surface 100 b of the cone-shaped nut 100, and the liquid droplets of the lubrication fluid are discharged from the infinitesimal flow rate pump 401 provided at the MEMS element 40 to the axial end surface 100 b so that the relative speed between the liquid droplet and the axial end surface 100 b as the surface to which the liquid droplets adhere can be further decreased. As a result, the lubrication fluid can reliably adhere to the axial end surface 100 b without the liquid droplets being blown away, and can be stably supplied to the bearing 8.

[7] In the vacuum pump according to [6], the MEMS element has a temperature sensor configured to capture infrared light emitted from a surface of the rotor shaft or a surface of the lubrication path member as a temperature measurement target surface to measure a temperature, and an infrared light incident window that the infrared light guided by the temperature sensor enters. A first protection section configured to prevent adherence of the lubrication fluid to the infrared light incident window is further provided. As illustrated in FIG. 7, the tubular protection section 440 is provided to surround the periphery of the infrared light window 432 a so that adherence of the lubrication fluid to the infrared light window 432 a can be prevented and accurate temperature measurement can be reliably performed by the temperature sensor 432.

[8] The vacuum pump according to [7] further includes a second protection section configured to prevent adherence to the temperature measurement target surface. For example, the protection section 440 illustrated in FIG. 7 or 8 functions as the second protection section, and prevents the liquid droplets of the lubrication fluid discharged from the infinitesimal flow rate pump 401 from adhering to the end surface 101 of the shaft 10 as the temperature measurement target surface. As a result, degradation of the temperature measurement value accuracy due to adherence of the lubrication fluid to the end surface 101 can be prevented.

[9] The vacuum pump according to any one of [1] to [8] further includes a flow rate sensor configured to detect the amount of lubrication fluid to be transferred by the infinitesimal flow rate pump, and a diagnosis section configured to make a diagnosis on the amount of lubrication fluid stored in the lubrication fluid storage section based on a detection result of the flow rate sensor. The arithmetic circuit 302 (see FIG. 6) functioning as the diagnosis section makes a diagnosis on the amount of lubrication fluid stored in the lubrication fluid storage section 60 based on the detection result of the flow rate sensor 431. Using such a diagnosis result, failure due to a lack of the lubrication fluid in the lubrication fluid storage section 60 can be avoided, for example.

Various embodiments and variations have been described above, but the present invention is not limited to these contents. These embodiments and variations may be combined. Other aspects conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention. For example, the turbo-molecular pump configured such that the rotor shaft of the pump rotor is supported by the bearing lubricated with the lubrication fluid has been described as the vacuum pump, but the present invention is not limited to the turbo-molecular pump. The present invention is similarly applicable to a vacuum pump configured such that a rotor shaft of a pump rotor rotating at high speed is supported by a rolling bearing lubricated with lubrication fluid. 

What is claimed is:
 1. A vacuum pump comprising: a rolling bearing configured to support a rotor shaft provided at a pump rotor; a lubrication fluid storage section configured to store lubrication fluid to be supplied to the rolling bearing; a MEMS element including, at a rotor-shaft-side lubrication fluid circulation path in a lubrication fluid circulation path between the rolling bearing and the lubrication fluid storage section, an infinitesimal flow rate pump configured to discharge a liquid droplet of the lubrication fluid; and a first flow path of a capillary structure configured to move the lubrication fluid of the lubrication fluid storage section to the infinitesimal flow rate pump by capillary force.
 2. The vacuum pump according to claim 1, further comprising: a lubrication path member provided adjacent to the rolling bearing at the rotor shaft and having a conical surface forming part of the lubrication fluid circulation path, wherein a radius of the conical surface from a center of the rotor shaft is set greater toward the rolling bearing, and the lubrication fluid discharged from the infinitesimal flow rate pump and adhering to the conical surface is moved in a direction of the rolling bearing on the conical surface by centrifugal force.
 3. The vacuum pump according to claim 1, wherein the infinitesimal flow rate pump is configured to discharge the lubrication fluid to the rolling bearing.
 4. The vacuum pump according to claim 1, further comprising: at least one of a vibration sensor configured to detect vibration of the rolling bearing or a temperature sensor configured to perform non-contact detection of a temperature of the lubrication fluid circulation path; and a control section configured to drivably control the infinitesimal flow rate pump based on a detection result of at least one of the vibration sensor or the temperature sensor, thereby controlling an amount of the lubrication fluid to be transferred by the infinitesimal flow rate pump.
 5. The vacuum pump according to claim 4, further comprising: a warning section configured to output deterioration information on the rolling bearing based on the detection result of at least one of the vibration sensor or the temperature sensor.
 6. The vacuum pump according to claim 1, further comprising: a lubrication path member provided adjacent to the rolling bearing at the rotor shaft, wherein the lubrication path member has a conical surface forming part of the lubrication fluid circulation path, and an axial end surface connected to the conical surface and forming another part of the lubrication fluid circulation path, and the MEMS element provided with the infinitesimal flow rate pump is arranged facing the axial end surface, and the liquid droplet of the lubrication fluid is discharged from the infinitesimal flow rate pump to the axial end surface.
 7. The vacuum pump according to claim 6, wherein the MEMS element has a temperature sensor configured to capture infrared light emitted from a surface of the rotor shaft or a surface of the lubrication path member as a temperature measurement target surface to measure a temperature, and an infrared light incident window that the infrared light guided by the temperature sensor enters, and a first protection section configured to prevent adherence of the lubrication fluid to the infrared light incident window is further provided.
 8. The vacuum pump according to claim 7, further comprising: a second protection section configured to prevent adherence to the temperature measurement target surface.
 9. The vacuum pump according to claim 1, further comprising: a flow rate sensor configured to detect an amount of the lubrication fluid to be transferred by the infinitesimal flow rate pump; and a diagnosis section configured to make a diagnosis on an amount of the lubrication fluid stored in the lubrication fluid storage section based on a detection result of the flow rate sensor. 